Photovoltaics is the field of science related to generating electrical power by converting light energy into electrical current using conductors that exhibit the photovoltaic (PV) effect. In most PV applications, the light energy is radiation from sunlight and, for this reason, PV devices are typically referred to as solar cells. Photovoltaic power generation normally employs one or more solar panels, each of which comprises a number of solar cells. Each solar cell includes a photoemissive material that exhibits a property known as the photoelectric effect, wherein which the material absorbs photons of light and, once exposed to electromagnetic radiation above a certain threshold frequency, reactively emits or ejects electrons. The resultant flow of electrons generates an electric current, which can be used as electrical power. Some materials presently employed by PV cells include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium selenide/sulfide.
A solar PV array typically comprises an arrangement of strings of electrically-connected PV panels. A string in the context of PV arrays can be an arrangement of PV panels connected together in series. A PV array is generally composed of multiple strings of PV panels. Each string output can be received in a device known as a combiner, which “combines” the current from each string into a larger conductor, called a feeder. The feeder feeds downstream equipment (e.g., the direction of current flow away from the PV panel(s)), such as disconnect switches, possibly other lower-level combiners, and ultimately to an inverter. The inverter can be a DC-to-AC inverter that converts the DC currents produced by each string of the PV array into a corresponding AC current. The combiner can receive strings from one or more PV arrays.
A practical arc fault detection system is typically designed to distinguish between normal arcing and destructive arcing. Normal arcing may occur between surfaces designed to control arcing, such as switching contacts, motor commutators, and fuse elements. Destructive arcing generally occurs through failed insulating material or through air between surfaces not intended to control arcing. When the wattage becomes sufficiently large, for example 600 Vac per pole and 600 Vdc through two pole (300 Vdc/Pole) across an electrical switch, the electron flow across switch contacts can be sufficient to ionize the air molecules between the contacts as the switch is opened or closed, forming a normal electric arc. There are various conditions that may cause a destructive arc fault, such as insufficient contact pressure, electrical stress from repeated overloading, corroded, worn, or aged wiring or insulation, etc. Electrical arcing can occur at various locations in the photovoltaic system, for example, in the solar cell panels, distribution wiring, disconnect panels, inverter, and/or branch circuit wiring. Different types of arcing that may occur include series (e.g., arcing across a broken conductive path), parallel (e.g., arcing through damaged insulation), and faults to ground (e.g., arcing to grounded components).
The electric arc is very hot and may damage insulation, wiring, and other components in the PV system. Current solutions being pursued for mitigating arc faults in PV systems include opening of the circuit at the combiner box or turning off the inverter if an arcing fault is detected on the system. This method can be effective for series faults within the system, but is generally not effective for parallel faults between circuit conductors or the circuit conductors to ground. In these scenarios, opening the circuit could potentially increase the energy in the arc path, which can aggravate the situation. Methods of shorting the output of solar panels have also been attempted, but may induce additional stresses on series arcing fault hazards. There is therefore a need for more effective and efficient arc fault mitigation in photovoltaic installations.